Effect of carbon nanotube length on the piezoresistive response of poly (methyl methacrylate) nanocomposites

Multiwall carbon nanotubes (MWCNTs) were systematically fragmented using high density ultrasonic energy and used as fillers of a poly (methyl methacrylate) matrix (PMMA). MWCNT fragmentation was confirmed by scanning electron microscopy and atomic force microscopy. Dedicated MWCNT length measurements yielded a log-normal statistical distribution, with mean value of 1.33 gm for the as-received MWCNTs and 0.66 mu m for the fragmented MWCNTs. Higher electrical percolation threshold and lower electrical conductivity were obtained for MWCNT/PMMA composites (0.01-1 wt.% MWCNT concentration) using the fragmented MWCNTs. Higher electro-mechanical (piezoresistive) sensitivity under tensile tests was measured for PMMA nanocomposites with fragmented MWCNTs, which was explained by a competition of mechanisms related to the MWCNT length.